Abstract

Spotted gum (Corymbia citriodora subspecies Variegata) has the potential to be the major hardwood species for large-scale plantations in South East Queensland, Australia, but production research is limited due to the lack of age of research plots. Optimal spacing is a major subject of concern. Based on time series data from a spotted gum experiment site, growth performance is analysed for five spacing levels: ─11.3 m x 11.3 m (78 stems per hectare), 7.4 m x 7.4 m (182 sph), 5.4 m x 5.4 m (343 sph), 3.6 m x 3.6 m (771 sph) and 2.9 m x 2.9 m (1189 sph). The major objective was assumed to be to maximise total merchantable log volume. A growth model was produced, and the mean diameter at breast height (dbh) and total merchantable log volume for each spacing levels at a range of harvesting ages was estimated. From the analysis, the spacing level of 5.4 m x 5.4 m was found to be optimal for maximising merchantable log volume to 10 cm small-end diameter. Further analysis of mean dbh, height and volume of the largest 200 and 250 trees from this spacing level indicates that merchantable log volume could be maximised by retaining the 250 largest trees per hectare. The total financial revenue from the best spacing level in 25 and 30 years are predicted to be $13,637 and $17,779 per hectare, respectively. If full rotation data could be obtained, more reliable models could be produced, and a more accurate financial estimate could be made.